1. Field of the Invention
The present invention relates generally to a disk drive of a perpendicular magnetic recording system using a single magnetic pole type head and, in particular, to a servo write method for recording servo data on a disk.
2. Description of the Related Art
In recent years, attention has been paid to the perpendicular magnetic recording system as a technique for overcoming the limitation of recording density in the longitudinal magnetic recording (in-plane magnetic recording) system, in the field of a magnetic disk drive represented by a hard disk drive. In this perpendicular magnetic recording system, the recent tendency has been toward promoting the practical use of a disk drive of a type using a disk of a double-layered structure as a data recording medium.
A disk with such a double-layered structure has a recording magnetic layer revealing a perpendicular magnetic anisotropy and a soft magnetic layer formed between the recording magnetic layer and a substrate. The soft magnetic layer has the function of creating a closed magnetic path of a magnetic flux generated in one magnetic pole of a head to the other magnetic pole at the time of recording data.
In the disk drive of the perpendicular magnetic recording system, use has been made of, as a read head, an active element represented by an MR (magnetoresistive) element (including a GMR element) as in the case of the longitudinal magnetic recording system, while, on the other hand, use is made of, as a write head, a ring type head or a single magnetic pole type head as in the case of the longitudinal magnetic recording system. In general, use is made, in the disk drive, of a magnetic head having a read head and write head mounted in a separate way on one slider.
The ring type head can be used for either the perpendicular magnetic recording system or the longitudinal magnetic recording system. The single magnetic pole type head, on the other hand, has been developed as a write head for perpendicular magnetic recording only. If, therefore, the practical use of the perpendicular magnetic recording system is promoted, there is a high possibility that many more single magnetic pole type heads are employed.
In short, with the above-mentioned trend thus promoted, there is a high possibility that, as the disk drive of a perpendicular magnetic recording system, the mainstream will be toward adopting a drive using a disk of a double-layered structure as a data recording medium as well as using a single magnetic pole type head as the write head.
It is well known that, in the manufacturing process of a disk drive, a servo write step is done for recording servo data on the disk in servo areas. The servo data is used, prior to a read/write operation, to control the positioning of a head (read/write head) to a target position (a track to be accessed) on a disk.
Generally, in the servo write step, a dedicated device called a servo track writer (STW) is used to perform recording processing of servo data on a disk drive with a drive mechanism for a head, disk etc., assembled thereon. In the disk drive of a longitudinal magnetic recording system, the recording processing of the servo data by the STW is normally carried out.
In the perpendicular magnetic recording system, no practical disk drive has been developed as a manufactured product to this day except for an experimental drive. There is no actual report that the recording processing of servo data is carried out by a servo write step of any practical stage. In particular, in the disk drive of a perpendicular magnetic recording system using a single magnetic pole type head and disk of a two-layered structure, no servo write step of any practical stage has been achieved though such a disk drive will be able to be realized as a near-future mainstream product.